1. Field of the Invention
The present invention relates to a piezoelectric resonator comprising a base through which pass two conducting posts electrically isolated therefrom and a piezoelectric plate comprising a central active zone surrounded by a peripheral ring connected to the central zone by at least two bridges defining slits separating the central zone from the peripheral ring, each face of the central zone being covered with an adherent electrode extending through one at least of the bridges over a part of the peripheral rings, each electrode of the plate being connected to one of the conducting posts through a conducting fixing means.
2. Description of the Prior Art
Resonators of this type have been described in French Patent Applications Nos. 83/15 652 entitled "High Overvoltage Self Suspended Resonator", 83/15 653 entitled "Resonator With Low Acceleration Sensitivity" and 83/15 654 entitled "Piezoelectric Resonator for Severe Environment", which applications were filed jointly by the applicant on Sept. 30, 1983. The contents of these different applications are incorporated by reference in the present application.
These different piezoelectric resonators are held secured to the base by conducting posts passing through said base and electrically connected to the electrodes of the piezoelectric plate on the external edge of the peripheral ring of said plates. However, in practice, so as to reduce production costs, commercially available bases are generally used whatever the dimensions of the piezoelectric plates fixed inside the case. It has generally been discovered that the diameter of these piezoelectric plates is different and in most cases greater than the diameter at which the posts of the base are disposed. The result is that the means for fixing the posts to the quartz plate are formed from metallic wires or ribbons slanted with respect to the direction of said posts. It has generally been noted that the performance of the resonators, using the above fixing methods, are fairly mediocre as regards sensitivity to acceleration. Generally, for a traditional quartz plate, i.e. not provided with slits as in the case of the present invention, the sensitivity to accelerations of the resonators thus obtained is not less than 1.times.10.sup.-9 /G. In addition, such a value of sensitivity to acceleration is not easily reproducible from one resonator to another. When piezoelectric plates are used having slits in accordance with the above mentioned application 83/15 653, this sensitivity to acceleration is considerably increased since a sensitivity is obtained less than 1.times.10.sup.-9 /G. But, as in the preceding case, and although the overall results are improved, a great dispersion of this sensitivity value is noted in the same manufacturing batch.
So at the present time there exists no system for fixing the piezoelectric plates to the posts of the base so as to obtain accelerometric sensitivities less than 1.times.10.sup.-9 /G with good reproducibility of the value of the sensitivity to acceleration.